Slagging in top blown converters

ABSTRACT

Nonferrous mattes containing iron are treated to slag iron therefrom. A bath of the matte is established and the iron content thereof is lowered to about 10 percent. When the iron content of the matte has been lowered to about 10 percent, a turbulent bath of the matte is treated with an oxygen-transfer slag containing about 25% to 35% SiO2 and 5% to 35% Fe2O3 while surface blowing the slag with a free-oxygen-containing gas to lower the iron content of the matte to less than about 1 percent. Advantageously, the final stages of iron removal are conducted at temperatures in excess of about 1,250* C.

United States Patent 723,500 3/1903 Thofehrn inventors Appl. No.

Filed Patented Assignee SLAGGING 1N TOP BLOWN CONVERTERS 28 Claims, 1 Drawing Fig.

IU.S. Cl 75/75, 75/63, 75/82 llnt. Cl C221) 7/00, C 213 15/14, C22b 23/06 Field of Search 75/21, 75, 82, 63

References Cited UNITED STATES PATENTS Kenworthy Aiken Borchers Grebe ABSTRACT: Nonferrous mattes containing iron are treated to slag iron therefrom. A bath of the matte is established and the iron content thereof is lowered to about 10 percent. When the iron content of the matte has been lowered to about 10 percent, a turbulent bath of the matte is treated with an oxygentransfer slag containing about 25% to 35% SiO- and 5% to 35% Fe O while surface blowing the slag with a free-oxygencontaining gas to lower the iron content of the matte to less than about 1 percent. Advantageouslly, the final stages of iron removal are conducted at temperatures in excess of about been lowered to less than about SLAGGING lN TOP BLOWN CUNVTIERS The present invention relates to the treatment of nonferrous mattes and sulfide ores or ore concentrates to remove iron therefrom, and more particularly to the pyrometallurgical treatment of nonferrous mattes and sulfide ores or ore concentrates to oxidize and remove iron by slagging.

Twenty years after Bessemer developed his pneumatic process for convening iron to steel, Pierre Manhes developed aprocess for pneumatically converting white metal to blister copper. The pneumatic process for converting iron to steel could not be directly applied Peirce-Smith the conversion of white metal to blister copper primarily because of mechanical and thermal considerations. Manhes taught that white metal could be converted to blister copper if a free-oxygen-containing gas were continually introduced into the upper sulfide phase, and not in the lower metal phase, and solved the problem by employing a side blown converter which could be rotated so that the tuyeres were always placed in the sulfide phase. If a free-oxygen-containing gas were introduced into the metal phase, the bath at the tuyeres froze, blocking them and stopping the reaction. Since the inception of Manhess basic concept it has been applied as standard practice, e.g., the Peirce-Smith converter. No radical departures from Manhess process have occurred, such changes as have been made being in the areas of furnace refractory selection, size and shape, tuyere design, and choice of flux materials. Although Manhes's device has been the workhorse of the nonferrous industry, as exemplified by copper and nickel practice, it has a number of significant shortcomings. These are inherent in its limited operational capabilities relating to gas-liquid-solid contact, introduction of gases having high oxidizing potentials and temperature control.

During the entire operating cycle of Peirce-Smith converters, steep temperature and compositional gradients are established. The steep temperature gradients are characterized by undesired high temperatures in the tuyere zone and objectionably low temperatures at locations remote therefrom. Localized high temperatures near the submerged gas inlets accelerate refractory and tuyere wear and unduly low temperatures elsewhere contribute to precipitation of magnetite which increases metal loss in slag and can lower converter capacity by the build up of accretions on the lining. The loss of nonferrous metal values to the slag is a serious problem requiring treatment of all of the slag for recovery purposes.

Various suggestions have been set forth, and some of these practiced, to overcome the shortcomings of the Peirce-smith converters. For example, oxygen-enriched air Other objects and advantages will become apparent from the following description taken in conjunction with the FIGURE which is an equilibrium diagram depicting the liquidus relationships in the ternary system of F e O -F eO-SiO at those temperatures which are of interest in slagging iron from nonferrous sulfides.

Generally speaking, the present invention contemplates a process for slagging iron from sulfide materials containing iron and at least one nonferrous metal selected from the group consisting of nickel, copper and cobalt. The process comprises providing a turbulent bath of a sulfide material which contains less than about percent iron; providing and maintaining a liquid slag substantially saturated with silica to lower the chemical potential of FeO and the potential for precipitation of solid magnetite in contact with the turbulent bath; surface blowing the slag with a free-oxygen-containing gas to maintain the slag oxidizing to iron contained in the turbulent bath whereby the slag selectively oxidizes iron in the turbulent sulfide bath to FeO, which FeO is then dissolved in the slag; maintaining the sulfide bath and slag in a state of turbulence for good liquid-liquid contact so that concentration gradients within each phase are minimized and so that any oxidized nonferrous metals in the slag can be reduced by the iron in the bath and continuing surface blowing with the free-oxygencontaining gas until the iron content of the turbulent bath has 1 percent.

Most generally, sulfide materials, which can be treated in accordance with the process of the present invention, will contain more than about 10 percent iron. These materials can be treated by surface blowing the turbulent bath of the sulfide material with a free-oxygen-containing gas to oxidize iron in the bath; providing and maintaining a liquid slag substantially saturated with silica to lower the chemical potential of FeO and the potential for precipitation of solid magnetite over and in contact with the turbulent sulfide bath at least when the iron content of the turbulent sulfide bath has been lowered to less than about 10 percent so that the free-oxygen-containing gas maintains the slag oxidizing to :iron contained in the turbulent sulfide bath whereby the slag selectively oxidizes iron in the turbulent sulfide bath to FeO, which FeO is then dissolved in the slag; maintaining the sulfide bath and slag in the state of turbulence so that concentration gradients within each phase are minimized and so that any oxidized nonferrous metals in the slag can be reduced by iron in the sulfide bath and continuing the surface blowing with the free-oxygen-containing gas until the iron content of the turbulent sulfide bath has been lowered to less than about 1 percent.

Sulfide materials containing iron and at least one nonferrous value selected from the group consisting of nickel, copper and cobalt in the form of matter, ores or ore concentrates can be treated in accordance with the process of the present invention. Although most generally the process will be applied to copper, copper-nickel or nickel mattes and sulfide ores and ore concentrates the process can also be employed to treat sulfidic materials containing lead with appropriate changes in the temperatures and slag compositions being made. Furthermore, oxide ores which contain any of the foregoing nonferrous metals and which have been sulfided to produce a sulfide intermediate or matte can also be treated in accordance with the present invention. Also, scrap containing metal values can be treated in accordance with the process of the present invention, e.g., by its direct addition to the sulfide bath. The terms sulfide material" and sulfide bath" when used herein refer to materials containing iron, at leastone nonferrous metal selected from the group consisting of nickel, copper and cobalt and sulfur in amounts at least sufficient to combine with the nonferrous metals. The materials often contain sulfur in amounts sufficient to combine with all the iron as well as all the nonferrous metals, but synthetically produced mattes, in which the amount of sulfur can be insufficient to combine with all of the iron, can be treated in accordance with the process of the present invention. Since the amount of sulfur in the sulfide bath can be insufficient to combine with all of the iron and because of the ionic nature of molten mattes, it will be understood that when the term iron contained in the bath" is employed, this terminology will refer to iron in the bath whether or not it is accompanied by a stoichiometric quantity of sulfur for the formation of FeS. it will also be noted that all compositions referred to herein are given on a weight basis unless otherwise noted.

Advantageously, a rotating cylindrical furnace, which is lined with a suitable refractory, is employed for slagging. Although the rotating furnaces can be mounted substantially horizontally, it is advantageous to have the rotating furnace inclined along its longitudinal axis to provide even greater turbulence. The cylindrical furnace is advantageously closed at one end to maximize its thermal efficiency and the other end is provided with a lance for surface blowing the sulfide bath or slag with a free-oxygen-containing gas, a burner to vary operating temperatures and atmosphere composition and a hood to collect off-gases. It will be noted that the term "surface blowing as used herein refers to the technique of introducing gas into the sulfide bath or into the slag by tuyereless blowing from above the upper surface of the bath or slag and does not necessarily imply the stream of gas does not penetrate the upper surface of the bath or slag. The furnace is provided with rotating means so that it can be rotated at speeds which provide the desired bath turbulence. The turbulence enhances heat transfer, increases the overall rate of the chemical reactions, minimizes compositional gradients within each phase, and significantly reduces diffusion barriers between the slag and the sulfide phasei. Other furnace designs can be employed but such furnaces must be provided with means for delivering the gas to the slag and must also provide the desired agitation by mechanical, electromechanical or other suitable means.

An important feature of the present invention is the tuyereless introduction of oxygen to the molten sulfide bath, particularly when the iron content of the sulfide bath is below about percent when oxygen is introduced via the slag. Since submerged tuyeres are not employed and the bath is independently maintained in a turbulent condition, gases with highfree-oxygen contents such as commercial oxygen and oxygenenriched air can be employed without encountering the problems often associated with refractory wear in the submerged tuyere. Introduction of oxygen to the molten sulfide bath through the siliceous slag, particularly when the iron content of the sulfide bath is less than about 10 percent, provides slags with lower nonferrous values than heretofore realized in conventional practice. A possible explanation for the lower contents of nonferrous metal values in the slag as compared with those obtained in Peirce-Smith converters, although the present invention is not limited thereto, is that oxygen introduced into the sulfide phase via the slag has a lower chemical potential and is therefore more selective in oxidation processes. The more selective nature of these oxygen-transfer slags is of particular importance when the iron content of mattes is below about 10 percent since the chemical potential of iron in the matte is decreasing while the chemical potential of more oxidizable nonferrous metals such as cobalt approach the chemical potential of iron with the result that high-oxygen potentials become less selective and such nonferrous metals are oxidized and lost to the slag. In conventional Peirce-Smith practice gaseous oxygen is injected directly into the sulfide phase at a high-chemical potential. As the rising bubble oxidizes the adjacent sulfide, its oxygen content is gradually converted to sulfur dioxide but the chemical potential of the residual oxygen is still relatively high and quite capable of oxidizing FeO to Fe o, or some nonferrous values to oxides. As the iron content of the sulfur bath decreases, the likelihood that metals other than iron will be oxidized increases. In the process of the present invention the slag delivers oxygen at a low chemical potential which is well suited for oxidizing iron to FeO but not substantially further and has less tendency to oxidize nonferrous metals in the bath. Furthermore, any FeO generated is produced at the slag-matte interface where it can be quickly taken into solution by the slag with reduced likelihood of further oxidation. The greater efficiency of the converting operation may also be explained in terms of the chemical potential of oxygen in the slag in that since the oxidation process via the slag is more selective, little solid magnetite, which endothermically and only sluggishly reacts with iron in the matte, is formed in the matte. It is believed, although the invention is not limited thereto, that iron dissolved in the slag in the ferrous state is partially oxidized to the ferric state during treatment with the free-oxygen-containing gas which ferric iron is the effective oxygen carrier and that the sulfide phase, which is maintained in a state of agitation or turbulence, is oxidized by the ferric iron in the slag at the slagsulfide bath interface.

The chemical character of the slag will exert a great influence on both the efficiency and extent of the oxidation and slagging of iron from the sulfide phase. In practicing the process of the present invention it is believed, although the invention is not limited thereto, that ferric iron dissolves in the slag is the efi'ective oxygen carrier and that the slag should contain sufficient ferric iron to oxidize iron sulfide in the matte. During oxidation and slagging of iron from the matte, sulfur dioxide is evolved and equilibrium calculations which show evolution of high (superatmospheric) partial pressures of sulfur dioxide indicate that the reaction is highly favorable whereas low partial pressures suggest the reaction is highly unfavorable. It can be shown that silicate slags containing substantial amounts of ferric iron when brought to equilibrium with an iron sulfide-containing matte will produce high sulfur dioxide partial pressures whereas slags containing only minor amounts of ferric iron will produce but low sulfur dioxide partial pressures. For example, when treating a copper matte con taining 30 percent copper, 40 percent iron and 30 percent sulfur at l,300 C., the equilibrium partial pressure of sulfur dioxide released in the presence of a magnetite-saturated slag is 1X10 times greater than the equilibrium sulfur dioxide partial pressure obtained by treating a matte of the same composition with a slag containing only 1 percent ferric oxide. Another important aspect of the chemical character of the slag is the amount of wiistite (FeO) in the slag, particularly when it is desired to insure low-iron contents in the final matte. In order to insure low-iron contents in the matte, the FeO in the slag should have a low-chemical potential since low-FeO chemical potentials in the slag insure that FeO produced by the oxidation of iron in the matte is more readily dissolved in the slag and less likely to be oxidized further. During iron oxidation and slagging it is advantageous, particularly during the later stages thereof, to employ silica-saturated slags. Best results for iron oxidation and slagging for most of the operation are achieved by providing a slag nearly saturated with magnetite and silica and even better results are obtained by using such slags at higher temperatures, e.g., above about l,300 C. or even better above about l,400 C. However, during the later stages of iron removal the oxidizing potential of the slag is advantageously lowered percent diminish losses of nonferrous values to the slag.

A clearer understanding of the oxygen-transfer slags which can be employed in the process of the present invention can be gained by reference to the FIG., which depicts a ternary equilibrium diagram of silica (SiO,), wiistite (FeO) and ferric oxide mo at various temperatures for compositions that are useful as refining slags. The area bounded by ABCDE represents compositions that are liquid at various temperatures, which compositions are specifically shown by lines with temperatures marked thereon. In three-dimension the area ABCDE actually represents surfaces with specific surfaces being represented, for example, by ABCFG and CDJI-IF. The line CF, which is the intersection of surfaces ABCFG and CDJI-IF represents slags with the greatest oxidizing potential and with low-FeO potentials by virtue of its saturation with magnetite and with silica. For example, at 1,400 C. a slag having a composition represented by point P, i.e., about 40 percent FeO, about 33 percent Fe,0;, and about 27 percent SiO,, would have the greatest oxidizing potential. However, since FeO is produced by reduction of Fe,0 in the slag and by oxidation of iron in the matte, provisions must be made to insure that sufiicient SiO, is present to dissolve the FeO produced and minimize the possibility of overoxidizing it to solid mo, Furthennore, in commercial practice it would be impractical to attempt to maintain the slag composition within such a narrow range. Therefore, for both practical and theoretical considerations it is advantageous to employ excess quantities of SiO,. As the FIGURE also shows, slags with similar compositions have a greater dissolving power for Fe o, at higher temperatures and such higher temperatures thereby minimize precipitation of solid magnetite. The oxygen-transfer slags in accordance with the present invention advantageously contain at least about 25 percent and not more than about 35 percent SK), and from about 5 percent to 35 percent Fe,O Even more advantageously, the slag composition is controlled at about 30 percent to 35 percent SiO,. With slags containing the foregoing amounts of silica and Fe,0, the precipitation of solid magnetite is minimized while dissolution of FeO and the oxidizing power of the slag are maximized.

Another important feature of the present invention is the turbulent state of the molten sulfide bath which turbulence minimizes concentration gradients within the individual phases. Many authorities suggest that at the conditions prevailing in high-temperature metallurgy chemical equilibrium is almost instantaneously achieved. Although chemical equilibrium may be instantaneously achieved in some pyrometallurgical processes, the rate of attainment of equilibrium in processes in which two immiscible phases are involved is dependent on chemical transport, i.e., diffusional processes, and can be quite slow. When diffusion processes are solely relied on for transport, films with compositions approaching equilibrium compositions are established and the rate of approach to equilibrium is slowed down due to the absence of high driving forces. in order to overcome the effects of diffusion films or barriers, the reacting substances must be adequately mixed to minimize the thickness of such barriers, i.e., the sulfide bath and silicate slags must be maintained in a state of turbulence. Thus, the process of the present invention requires that independent agitation be applied to the molten bath in order to provide a turbulent bath for highly efficient operation. It might be noted that the turbulence of the molten bath increases the gas-slag interface area to thereby render absorption of the free-oxygen-containing gas in the slag more efficient. Furthermore, when the process is conducted in a cylindrical rotating furnace, slag, which is carried from the bath by the rotating refractory, drops off the refractory and produces a rainlike effect which also increases gas-slag contact, thus aiding oxygen absorption from the furnace atmosphere.

As noted hereinbefore, it is advantageous to employ a cylindrical rotating furnace rotated at speeds sufficient to produce a turbulent bath so that high thermal and chemical efficiencies are realized. An equally important consideration in employing rotating furnaces, particularly in commercial applications where deep baths are formed, is that the rotating refractory of the furnace provides sites for nucleating sulfur dioxide bubbles. In present copper practice, i.e., side blowing, both the refractory in the vicinity of the tuyeres and the injected gases themselves provide sites for nucleating sulfur dioxide bubbles which are then expelled from the bath so that by constantly removing a product of reaction the converting action can continue. When slag is employed to oxidize iron in the matte, injected gases are not available for nucleation and positive steps must be taken to insure nucleation and expulsion of sulfur dioxide bubbles. The process in accordance with the present invention insures the requisite nucleation by the turbulent bath concept. A turbulent bath insures that matte containing sulfur dioxide is constantly brought into contact with the refractory by the mixing action so provided. in addition, when the process is conducted in a rotating furnace, the rotating refractory constantly drags atmospheric gases beneath the surface of the molten bath, and along with the natural nucleation sites inherent in refractories effectively provides sulfur dioxide nucleation. It is also possible that the turbulence within the bath creates localized regions of pressure and rarefaction so that in the localized regions of rarefaction the critical nucleus size of sulfur dioxide is lowered to such an extent that nucleation sites are not required. From the foregoing it is seen that the turbulent bath serves three distinct functions-the turbulent bath minimizes steep concentration gradients within individual phases, insures rapid distribution of heat and insures the nucleation of gaseous products.

When the process of the present invention is conducted in a rotating furnace as described hereinbefore, the thermal efficiency and the ability to employ gases highly enriched with oxygen or to burn extraneous fuel allow the use of theoretically optimum but heretofore commercially unobtainable conditions. For example, when treating high-grade copper mattes it is now practical to heat the matte up to temperatures above about l,300 C. before commencing the blowing operation in order to avoid formation of undue amounts of magnetite in the sulfide and slag phases at the lower temperatures. Furthermore, semicontinuous smelting operations can be employed using an oxygen-enriched blast thereby minimizing heat losses due to nitrogen. For example, once the molten sulfide bath is formed and slagging is commenced solid matte, ore or ore concentrate, preheated if desired, can be continuously or intermittently added to the bath in addition to flux in order to utilize heat released by oxidation to smelt the solid materials. Extraneous fuel can also be combusted to perform this opera tion. Even more importantly, when slagging iron from copper mattes, high temperature and slags with high-silica content can be employed to minimize magnetite formation. Thus, when treating copper or coppernickel mattes, slags containing over about 30 percent Si0 and even much higher can be employed without impairing the fluidity of the slag since the high temperatures required to maintain the fluidity of the slag can be uniformly obtained. Advantageously, temperatures above about 1,300 C. and even much higher can be employed when treating copper mattes to minimize magnetite formation in the sulfide phase, decrease the stability of deleterious compounds such as ferrites and increase slagging rates. The lower slag viscosity results in smaller amounts of nonferrous metals mechanically entrapped in the slag. Of course, the conditions of temperature and slag compositions currently employed in conventional Peirce-Smith converters can be used but the use of such conditions will not result in the full benefits inherent in the practice of the present invention.

Higher temperatures are particularly important during the final stages of slagging since the chemical potential of iron is low and without the use of higher temperatures the iron sulfide in the matte will not be so readily oxidized by the slag. Not only are higher temperatures important in insuring low final iron contents in the matte, but higher temperatures are effective in increasing the kinetics of the slagging reactions and in avoiding the precipitation of magnetite from the matte phase. The slagging treatment is conducted at a temperature of at least about l,250 C. and advantageously at a temperature of more than about l,300 C. At these temperatures substantially complete oxidation of iron sulfide is obtained at highly attractive rates while avoiding or minimizing the problems associated with viscous slags and magnetite precipitation. If the slagging reactions are not suificiently exothermic to maintain the preferred operating temperature, additional heat can be supplied to the bath through an auxiliary burner by burning an extraneously added fuel with an excess of a free-oxygen-containing gas, e.g., air, oxygen-enriched air or commercial 0xygen, so that the oxidizing nature of the slag is not destroyed.

As noted hereinbefore, one of the advantageous features of the present invention is the selective oxidizing nature of the oxygen-transfer slags. When the sulfide material to be treated in accordance with the present invention contains more than about 10 percent iron, the molten sulfide bath can be surface blown with a free-oxygen-containing gas with or without a flux or slag and the surface blowing can be conducted in such a manner that the free-oxygen-containing gas completely penetrates the slag and directly oxidizes the matte until the iron content of the sulfide bath has been lowered to less than about 10 percent. This initial treatment to lower the iron content of the sulfide bath to less than about 10 percent can even be conducted in theabsence of independently supplied agitation, for example, in a stationary, e.g., L-D-type, converter. After the initial treatment to provide a sulfide bath containing less than about 10 percent iron has been completed, the sulfide bath is then treated with an oxygen-transfer slag to lower the iron content to less than about 1 percent while conducting the surface-blowing operation in such a manner that a preponderant part of the oxygen is introduced into the sulfide bath via the slag. When the iron content of the matte has been lowered to about 10 percent and oxidation is thereafter accomplished via the slag, the nature of surface blowing with the free-oxygen-containing gas may have to be altered to minimize direct oxidation of the matte via the free-oxygencontaining gas. Thus, the velocity of the gas or its angle of impingement can be altered to avoid contacting the matte directly with the free-oxygen-containing gas.

When substantially all the iron in the matte has been oxidized, the slag can be removed and blowing with a free-oxygen-containing gas can be resumed to convert the nonferrous sulfide to metal, e.g., blister copper, oxygen nickel or cupronickel. Alternatively, the resulting nonferrous sulfide can be tapped for subsequent treatment such as the slow cooling of a nickel-copper matte to effect a separation thereof or a nickel matte can be subjected to a liquid-liquid exchange process to remove various nonferrous contaminants, e.g., the removal of copper and cobalt from nickel sulfide.

The use of an oxygen-transfer slag in the final stages of iron removal is one of the advantageous features of the present invention in that iron oxidation via the slag is highly selective. However, as the iron content of the matte is lowered to about percent, the selectivity of slagging is lowered, particularly when the oxidizing potential for a specific slag composition is maintained at its maximum. As the iron content of the matte is lowered to about 5 percent, the selectivity of the slag can be maintained or regained by lowering the oxidizing potential of the slag. This can be accomplished by lowering the rate of blowing with the free-oxygen-containing gas or by lowering the oxygen content of the free-oxygen-containing gas, both of which result in replenishing the oxygen in the slag at a lower rate than it is consumed by reaction with iron in the matte. These treatments are conducted so that the oxidizing potential of the slag is lowered by about one to three orders of magnitude from its maximum oxidizing potential, e.g., the oxygen partial pressure of a silica-saturated slag at about 1,300 C. is lowered from about 6 atmospheres to 109 atmospheres. The embodiment of combusting a fuel is advantageous in that the thus-generated heat raises the temperature of the slag and the sulfide bath increasing the rate of reaction and the extent of iron removal while lowering the amount of sulfides entrained in the slag. The effectiveness of these treatments, i.e., whether the oxidizing potential of the slag has been sufficiently lowered to maintain the oxidizing selectivity thereof, can be ascertained by the amount of Fe O contained in the slag. For example, if it is desired to lower the oxidizing potential of a specific oxygen-transfer slag by two to three orders of magnitude from its maximum oxidizing potential, the Fe,0 content of a refining slag having a maximum oxidizing potential is lowered to between about 5 percent and 20 percent.

In carrying the invention into practice it is preferred to treat at least one nonferrous sulfide selected from the group consisting of nickel, copper and cobalt and containing iron to remove iron by oxidation and slagging which treatment comprises establishing a molten bath of the sulfide; surface blowing the bath with a free-oxygen-containing gas to lower the iron content to less than about 10 percent; providing and maintaining an oxygen-transfer slag containing between about 5 and 35 percent Fe,0, and silica in amounts sufficient to provide between about 25 percent and 35 percent silica over and in contact with the sulfide bath, at least after the iron content of the bath has been lowered to less than about 10 percent; maintaining the slag and sulfide bath at a temperature of at least about 1,250 C. surface blowing the slag with a free-0xygen-containing gas to maintain the slag oxidizing to iron in the sulfide bath; maintaining the sulfide bath and slag in a state of turbulence so that steep concentration gradients within individual phases at the slag-sulfide bath interface are minimized and so that sulfur dioxide bubbles are nucleated and removed from the sulfide bath and continuing the treatment with the free-oxygen-containing gas to slag substantially all the iron contained in the sulfide bath.

For the purpose of giving those skilled in the art a better understanding of the invention, the following illustrative examples are given:

Example 1 Approximately 6.5 metric tons of a sulfur-deficient nickel matte at a temperature of 1,260 C. and analyzing 25 percent nickel, 65 percent iron and 9 percent sulfur were charged into a rotary converter which measured about 4.4-meters long by 1.8 meters in diameter inside its magnesite chrome lining. The iron content of the matte was lowered to 10 percent by surface blowing with air at 95 percent oxygen efficiency through a water-cooled lance and the oxidized iron was slagged with quartz and sand which were added semicontinuously to maintain the SiO, content of the slag between 25 percent and 30 percent. At this point the matte was at a temperature of about l,300 C. and an oxygen-transfer slag containing about 15 to 18 percent Fe,0, and saturated with silica was employed to oxidize iron remaining in the matte. The slag was surface blown with air at lower rates and air velocities to avoid direct oxidation of the matte while maintaining the slag at its maximum oxidizing potential and silica was semicontinuously added to maintain the slag saturated with silica. In order to provide good liquid-liquid contact between the matte and the slag, the converter was rotated at 20 revolutions per minute to establish a turbulent bath. When the iron content had been lowered to about 2 percent, blowing with air was discontinued and natural gas was fully combusted to maintain the temperature of the bath at 1,300 C. and to lower the oxidizing potential of the slag, by not fully replenishing the oxygen therein, to between one to two orders of magnitude of its maximum oxidizing potential. The speed of rotation of the furnace was then lowered to about 5 revolutions per minute to enhance settling of entrained sulfides. Upon tapping, a matte analyzing 76 percent nickel, 0.8 percent iron and 20 percent sulfur was obtained and it was observed that no massive magnetite accretions appeared on the converter refractory.

Example 11 Approximately 6 metric tons of a copper matte analyzing 45.6 percent Cu, 5.2 percent Ni, 0.2percent Co, 26 percent Fe, and 23 percent S are charged into the rotary converter described above. The temperature of the bath is raised to 1,270 C. by combustion of extraneous fuel in a burner contained in the lance. Air is blown through the lance at a nozzle velocity of 240 meters per second while a mixture of quartz and sand is added semicontinuously to produce slags containing 25-30 percent silica. The temperature rises to 1,300 C. by the time the iron content is lowered to 10 percent. At this point, an oxygen-transfer slag containing about 15-18 percent rep, and saturated with silica is employed to oxidize the remaining iron in the matte. This is effected by decreasing nozzle velocity to meters per second to avoid direct oxidation of the matte while maintaining the oxygen potential of the slag near its maximum. As the iron content of the matte approaches 5 percent, the air rate is lowered to permit the Fe,0, content of the slag to gradually decrease. The slag is skimmed when the iron content is less than 1 percent and theresulting white metal is converted to blister copper.

It is to be noted that the present invention is not to be confused with prior processes which have conducted slagging and converting operations in rotary furnaces since these prior processes most frequently employed the rotary furnace to even out refractory temperatures. These prior processes required that the free-oxygen-containing gas be introduced into the sulfide phase and, therefore, did not recognize the importance of oxidizing via the slag, particularly during the latter stages of iron removal. Thus, these processes were not able to produce slags with low nonferrous metal value contents.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. For example, plumbiferous materials with treated in accordance with the process of the present invention. Such modifications and variations are considered to be within the purview and scope of the invention.

We claim:

1. A process for treating a sulfide containing iron and at least one nonferrous value selected from the group consisting of nickel, copper and cobalt'to remove iron which comprises providing a turbulent bath of the sulfide material which contains less than about 10 percent iron; providing and maintainappropriate modifications can be ing a liquid stag containing about 5 percent to 35 percent E c 19 glggrtli t 3 g-gent silica and the balance essentially FeO in contact with the turbulent sulfide bath; surface blowing the slag with a free-oxygemcontaining gas to maintain the slag oxidizing to iron contained in the turbulent sulfide bath whereby the slag selectively oxidizes iron in the turbulent bath to FeO, which lFeO is then dissolved in the slag; maintaining the sulfide bath and slag in a state of turbulence so that concentration gradients within each phase are minimized and so that oxidized nonferrous metals in the slag can be reduced by the iron in the sulfide bath and continuing surface blowing with the free-oxygemcontaining gas until the iron content of the turbulent sulfide bath has been lowered to less than about 1 percent.

2. A process as described in claim 1 wherein the sulfide bath and slag are maintained at a temperature above about l,250 C.

3. A process as described in claim and slag are maintained at 1 ,300 C.

A. A process as described in claim 1 wherein the slag is sub stantially saturated with silica to lower the chemical potential of FeO in the slag and the potential for precipitation of magnetite.

5. A process as described in claim ll wherein the slag contains between about 30 and 35 percent silica.

s. A process as described in claim ll wherein surface blowing of the slag is controlled to maintain the slag at its maximum oxidizing potential.

7. A process as described in claim 6 wherein after the iron content of the sulfide bath is lowered to less than about percent, surface blowing is controlled to lower the oxidizing potential of the slag by one to three orders of magnitude of its maximum.

b. A process as described in claim ll wherein a slag containing between about 5 and 35 percent Fe O between about 25 and 35 percent silica and the balance essentially FeO is em ployed to lower the iron content of the matte to less than about 5 percent and thereafter surface blowing is controlled to lower the Fe 0 content of the slag to between about 5 and 20 percent.

9. A process as described in claim 3 wherein the Fe O content of the slag is lowered to between about 5 and 20 percent by lowering the amount of oxygen in the free-oxygen-containing gas.

it). A process as described in claim 8 wherein the Fe O content of the slag is lowered to between about 5 and 20 percent by combusting a fuel above the slag.

11. A process for treating a sulfide containing iron and at least one nonferrous value selected from the group consisting of nickel, copper and cobalt to remove iron which comprises surface blowing a turbulent bath of the sulfide material with a free-oxygemcontaining gas to oxidize iron in the bath; providing and maintaining a liquid slag containing about 5 to 35 percent Fe O about 25 to 35 percent silica and the balance essentially FeO over and in contact with the turbulent sulfide bath at least when the iron content of the turbulent bath has been lowered to less than about 10 percent so that the free-oxygen-containing gas maintains the slag oxidizing to iron contained in the turbulent sulfide bath whereby the slag selectively oxidizes iron in the turbulent sulfide bath to FeO, which FeO is then dissolved in the slag; maintaining the sulfide bath and slag in the state of turbulence so that concentration gradients within each phase are minimized and so that oxidized nonferrous metals in the slag can be reduced by iron in the sulfide bath and continuing the surface blowing with the free-oxygen-containing gas until the iron content of the turbulent sulfide bath has been lowered to less than about 1 percent.

12. A process as described in claim lll wherein the sulfide bath and slag are maintained at a temperature above about 1,250C.

ll wherein the sulfide bath a temperature of at least about tial of FeO in the slag and the potential for precipitation of magnetite.

115. A process as described in claim it wherein the slag contains between about 30 and 35 percent silica.

16. A process as described in claim 11 wherein surface blowing of the slag is controlled to maintain the slag at its maximum oxidizing potential.

117. A process as described in claim 116 wherein after the iron content of the sulfide bath is lowered to less than about 5 percent, surface blowing is controlled to lower the oxidizing potential of the slag by one to three orders of magnitude of its maximum.

18. A process as described in claim 111 wherein a slag containing between about 5 and 35 percent Fe O between about 25 and 35 percent silica and the balance essentially FeO is employed to lower the iron content to less than about 5 percent and thereafter surface blowing is controlled to lower the t e- 0 to between about 5 and 20 percent.

19. A process as described in claim 18 wherein the Fe O, content of the slag is lowered to between about 5 and 20 percent by lowering the amount of oxygen in the free-oxygencontaining gas.

20. A process as described in claim 33 wherein the Fe O content of the slag is lowered to between about 5 and 20 percent by combusting a fuel above the slag.

21. A process for treating a sulfide containing iron and at least one nonferrous value selected from the group consisting of nickel, copper and cobalt to remove iron which comprises establishing a molten bath of the sulfide; surface blowing the sulfide bath with a free-oxygen-containing gas to lower the iron content to less than about l0 percent; providing and maintaining a slag containing between about 5 and 35 percent l e- 0 silica in amounts sufiicient to provide between about 25 and 35 percent silica and the balance essentially FeO over and in contact with the sulfide bath, at least after the iron content of the bath has been lowered to less than about 10 percent; maintaining the slag and sulfide bath at a temperature above about 1,250 C.; surface blowing the slag with a free-oxygen-containing gas to maintain the slag oxidizing to iron in the sulfide bath; maintaining the sulfide bath and slag in a state of turbulence so that steep concentration gradients within individual phases at the slag-sulfide bath interface are minimized and so that sulfur dioxide bubbles are nucleated and removed from the sulfide bath and continuing the treatment with the free-oxygen-containing gas to slag substantially all the iron contained in the sulfide bath.

22. A process as described in claim 21! wherein the sulfide bath and slag are maintained at a temperature of at least about 1 ,300 C.

23. A process as described in claim 21 wherein the slag contains between about 30 and 35 percent silica. I

24. A process as described in claim 21 wherein surface blowing of the slag is controlled to maintain the slag at its maximum oxidizing potential.

25. A process as described in claim 2d wherein after the iron content of the sulfide bath is lowered to less than about 5 percent, surface blowing is controlled to lower the oxidizing potential of the slag by one to three orders of magnitude of its maximum.

26. A process as described in claim 21 wherein a slag containing between about 5 and 35 percent IFe O between about 30 and 35 percent silica and the balance essentially R20 is employed to lower the iron content to less than about 5 percent and thereafter surface blowing is controlled to lower the Fe o to between about 5 and 20 percent.

27. A process as described in claim 26 wherein the Fe o content of the slag is lowered to between about 5 and 20 percent by lowering the amount of oxygen in the free-oxygencontaining gas.

content of the slag is lowered to between cent by combusting a fuel above the slag.

about and 20 per- 

2. A process as described in claim 1 wherein the sulfide bath and slag are maintained at a temperature above about 1,250* C.
 3. A process as described in claim 1 wherein the sulfide bath and slag are maintained at a temperature of at least about 1, 300* C.
 4. A process as described in claim 1 wherein the slag is substantially saturated with silica to lower the chemical potential of FeO in the slag and the potential for precipitation of magnetite.
 5. A process as described in claim 1 wherein the slag contains between about 30 and 35 percent silica.
 6. A process as described in claim 1 wherein surface blowing of the slag is controlled to maintain the slag at its maximum oxidizing potential.
 7. A process as described in claim 6 wherein after the iron content of the sulfide bath is lowered to less than about 5 percent, surface blowing is controlled to lower the oxidizing potential of the slag by one to three orders of magnitude of its maximum.
 8. A process as described in claim 1 wherein a slag containing between about 5 and 35 percent Fe2O3 between about 25 and 35 percent silica and the balance essentially FeO is employed to lower the iron content of the matte to less than about 5 percent and thereafter surface blowing is controlled to lower the Fe2O3 content of the slag to between about 5 and 20 percent.
 9. A process as described in claim 8 wherein the Fe2O3 content of the slag is lowered to between about 5 and 20 percent by lowering the amount of oxygen in the free-oxygen-containing gas.
 10. A process as described in claim 8 wherein the Fe2O3 content of the slag is lowered to between about 5 and 20 percent by combusting a fuel above the slag.
 11. A process for treating a sulfide containing iron and at least one nonferrous value selected from the group consisting of nickel, copper and cobalt to remove iron which comprises surface blowing a turbulent bath of the sulfide mAterial with a free-oxygen-containing gas to oxidize iron in the bath; providing and maintaining a liquid slag containing about 5 to 35 percent Fe2O3 about 25 to 35 percent silica and the balance essentially FeO over and in contact with the turbulent sulfide bath at least when the iron content of the turbulent bath has been lowered to less than about 10 percent so that the free-oxygen-containing gas maintains the slag oxidizing to iron contained in the turbulent sulfide bath whereby the slag selectively oxidizes iron in the turbulent sulfide bath to FeO, which FeO is then dissolved in the slag; maintaining the sulfide bath and slag in the state of turbulence so that concentration gradients within each phase are minimized and so that oxidized nonferrous metals in the slag can be reduced by iron in the sulfide bath and continuing the surface blowing with the free-oxygen-containing gas until the iron content of the turbulent sulfide bath has been lowered to less than about 1 percent.
 12. A process as described in claim 11 wherein the sulfide bath and slag are maintained at a temperature above about 1,250* C.
 13. A process as described in claim 11 wherein the sulfide bath and slag are maintained at a temperature of at least about 1, 300* C.
 14. A process as described in claim 11 wherein the slag is substantially saturated with silica to lower the chemical potential of FeO in the slag and the potential for precipitation of magnetite.
 15. A process as described in claim 11 wherein the slag contains between about 30 and 35 percent silica.
 16. A process as described in claim 11 wherein surface blowing of the slag is controlled to maintain the slag at its maximum oxidizing potential.
 17. A process as described in claim 16 wherein after the iron content of the sulfide bath is lowered to less than about 5 percent, surface blowing is controlled to lower the oxidizing potential of the slag by one to three orders of magnitude of its maximum.
 18. A process as described in claim 11 wherein a slag containing between about 5 and 35 percent Fe2O3 between about 25 and 35 percent silica and the balance essentially FeO is employed to lower the iron content to less than about 5 percent and thereafter surface blowing is controlled to lower the Fe2O3 to between about 5 and 20 percent.
 19. A process as described in claim 18 wherein the Fe2O3 content of the slag is lowered to between about 5 and 20 percent by lowering the amount of oxygen in the free-oxygen-containing gas.
 20. A process as described in claim 18 wherein the Fe2O3 content of the slag is lowered to between about 5 and 20 percent by combusting a fuel above the slag.
 21. A process for treating a sulfide containing iron and at least one nonferrous value selected from the group consisting of nickel, copper and cobalt to remove iron which comprises establishing a molten bath of the sulfide; surface blowing the sulfide bath with a free-oxygen-containing gas to lower the iron content to less than about 10 percent; providing and maintaining a slag containing between about 5 and 35 percent Fe2O3 , silica in amounts sufficient to provide between about 25 and 35 percent silica and the balance essentially FeO over and in contact with the sulfide bath, at least after the iron content of the bath has been lowered to less than about 10 percent; maintaining the slag and sulfide bath at a temperature above about 1,250* C.; surface blowing the slag with a free-oxygen-containing gas to maintain the slag oxidizing to iron in the sulfide bath; maintaining the sulfide bath and slag in a state of turbulence so that steep concentration gradients within individual phases at the slag-sulfide bath interface are minimized and so thaT sulfur dioxide bubbles are nucleated and removed from the sulfide bath and continuing the treatment with the free-oxygen-containing gas to slag substantially all the iron contained in the sulfide bath.
 22. A process as described in claim 21 wherein the sulfide bath and slag are maintained at a temperature of at least about 1, 300* C.
 23. A process as described in claim 21 wherein the slag contains between about 30 and 35 percent silica.
 24. A process as described in claim 21 wherein surface blowing of the slag is controlled to maintain the slag at its maximum oxidizing potential.
 25. A process as described in claim 24 wherein after the iron content of the sulfide bath is lowered to less than about 5 percent, surface blowing is controlled to lower the oxidizing potential of the slag by one to three orders of magnitude of its maximum.
 26. A process as described in claim 21 wherein a slag containing between about 5 and 35 percent Fe2O3 , between about 30 and 35 percent silica and the balance essentially FeO is employed to lower the iron content to less than about 5 percent and thereafter surface blowing is controlled to lower the Fe2O3 to between about 5 and 20 percent.
 27. A process as described in claim 26 wherein the Fe2O3 content of the slag is lowered to between about 5 and 20 percent by lowering the amount of oxygen in the free-oxygen-containing gas.
 28. A process as described in claim 26 wherein the Fe2O3 content of the slag is lowered to between about 5 and 20 percent by combusting a fuel above the slag. 